1. Field of the Invention
The present invention relates to an optical disk apparatus, an optical pickup, a preformatted signal generation method, and a program and is suitably applied to, for example, an optical disk apparatus compatible with an optical disk having a plurality of recording layers.
2. Description of the Related Art
Optical disk apparatuses developed at a rapid pace in recent years reproduce information by irradiating an optical disk such as a CD (Compact Disc), DVD (Digital Versatile Disc), and Blu-ray Disc (registered trademark, hereinafter referred to as the BD) with a light beam and reading a reflected light thereof.
On this optical disk, information to be recorded is recorded on tracks formed in a spiral fashion or concentrically after being encoded and modulated as pits or the like.
Thus, an optical disk apparatus condenses a light beam by an objective lens and, when information is reproduced from an optical disk, focuses the light beam on tracks formed in a spiral fashion or concentrically in a recording layer of the optical disk.
At this point, the optical disk apparatus receives a reflected light by providing, for example, a receiving region in a predetermined shape in a photo-detector. Then, based on a reception result thereof, the optical disk apparatus calculates a “focus error signal” and a “tracking error signal” representing shift amounts between the track that should be irradiated with the light beam (hereinafter, referred to as the “target track”) and the focus of the light beam in a focus direction and a tracking direction respectively.
Subsequently, the optical disk apparatus adjusts the focus of the light beam to the target track by moving the objective lens in the focus direction based on the focus error signal and also moving the objective lens in the tracking direction based on the tracking error signal.
Various methods such as the push-pull method and three-beam method are known as calculation methods of such a tracking error signal and further, a method called the one-beam push-pull method is also proposed (see, for example, Japanese Patent Application Laid-Open No. 2007-213754 (FIG. 15)).
On the other hand, when the optical disk apparatus records information on an optical disk or reproduces information from the optical disk, the optical disk apparatus acquires information about which position of an optical disk the target track on which the light beam is focused corresponds to (hereinafter, referred to as “address information”). Together with address information or instead of address information, “time information” representing an absolute time indicating an end position of recorded portions or a start position of non-recorded portions or a recording clock may be acquired. Information embedded in an optical disk in advance like the address information and time information is also called “preformatted information”.
Such address information or the like is recorded on an optical disk as preformats using grooves formed along tracks or “lands” between grooves formed also along tracks. For example, the “Land Pre-Pit (LPP) method” and “high-frequency wobble groove method (ADIP: Address In Pre-groove)” can be cited as addition methods of address information or the like.
When the LPP is used, pits are intermittently generated on a land and then, address information or the like is generated from a “pre-pit signal” obtained from such pits. When the ADIP is used, on the other hand, high frequencies are used as “wobble” frequencies formed by causing a groove to meander and address information or the like is generated from the phase of a “wobble signal” obtained from the wobble. In addition, an optical disk on which a signal such as a watermark is superimposed as address information or the like by a sequence of wobble added information pits is practically used.
Such a wobble signal or pre-pit signal is a signal preset on a recording track regardless of a recordable optical disk or read-only optical disk and is also called a “preformatted signal”. A light receiving element (photo-detector) to detect the preformatted signal is also used to detect a reproduced RF signal at the same time and, for a light receiving element divided into four parts, is frequently used also to detect a focus error signal or the like (see Japanese Patent Application Laid-Open Nos. 1993-128564 and 1994-290462).